This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The haloacid dehalogenase (HAD) superfamily is comprised of structurally homologous enzymes that share several conserved sequence motifs in their active site. The majority of HAD members are phosphohydrolases and may be divided into three subclasses depending on domain organization. In classes I and II, a mobile "cap" domain reorients upon substrate binding, closing the active site to bulk solvent. Members of the third class lack this additional domain. It is the cap domain that appears to be responsible for substrate specificity. My research has focused on understanding how this third class of enzymes that lacks the cap domain is able to recognize different targets. Protein PSPTO2114 from Pseudomonas syringae or "capless" is a novel protein with unknown function that by phylogenetic analysis, appears to be at the cross roads between class I and III HAD members. Based on sequence homology, it appears that bacillus cereus phosphonoacetaldehyde hydrolase (PHN), a class I HAD member, is the closest known X-ray structure, with only 24% sequence identity. "Capless" appears to share a similar dimerization domain that is present in PHN. The structure of capless wwill provide clues as to how this superfamily has evolved as well as providing insight to substrate specificity of the type III HAD members.